StdLib/LibC/Math/e_fmod.c

/* @(#)e_fmod.c 5.1 93/09/24 */
/*
 * ====================================================
 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
 *
 * Developed at SunPro, a Sun Microsystems, Inc. business.
 * Permission to use, copy, modify, and distribute this
 * software is freely granted, provided that this notice
 * is preserved.
 * ====================================================
 */
#include  <LibConfig.h>
#include  <sys/EfiCdefs.h>
#if defined(LIBM_SCCS) && !defined(lint)
__RCSID("$NetBSD: e_fmod.c,v 1.11 2002/05/26 22:01:49 wiz Exp $");
#endif

/*
 * __ieee754_fmod(x,y)
 * Return x mod y in exact arithmetic
 * Method: shift and subtract
 */

#include "math.h"
#include "math_private.h"

#if defined(_MSC_VER)           /* Handle Microsoft VC++ compiler specifics. */
  // unary minus operator applied to unsigned type, result still unsigned
  #pragma warning ( disable : 4146 )
#endif

static const double one = 1.0, Zero[] = {0.0, -0.0,};

double
__ieee754_fmod(double x, double y)
{
  int32_t n,hx,hy,hz,ix,iy,sx,i;
  u_int32_t lx,ly,lz;

  EXTRACT_WORDS(hx,lx,x);
  EXTRACT_WORDS(hy,ly,y);
  sx = hx&0x80000000;   /* sign of x */
  hx ^=sx;    /* |x| */
  hy &= 0x7fffffff; /* |y| */

    /* purge off exception values */
  if((hy|ly)==0||(hx>=0x7ff00000)|| /* y=0,or x not finite */
    ((hy|((ly|-ly)>>31))>0x7ff00000)) /* or y is NaN */
      return (x*y)/(x*y);
  if(hx<=hy) {
      if((hx<hy)||(lx<ly)) return x;  /* |x|<|y| return x */
      if(lx==ly)
    return Zero[(u_int32_t)sx>>31]; /* |x|=|y| return x*0*/
  }

    /* determine ix = ilogb(x) */
  if(hx<0x00100000) { /* subnormal x */
      if(hx==0) {
    for (ix = -1043, i=lx; i>0; i<<=1) ix -=1;
      } else {
    for (ix = -1022,i=(hx<<11); i>0; i<<=1) ix -=1;
      }
  } else ix = (hx>>20)-1023;

    /* determine iy = ilogb(y) */
  if(hy<0x00100000) { /* subnormal y */
      if(hy==0) {
    for (iy = -1043, i=ly; i>0; i<<=1) iy -=1;
      } else {
    for (iy = -1022,i=(hy<<11); i>0; i<<=1) iy -=1;
      }
  } else iy = (hy>>20)-1023;

    /* set up {hx,lx}, {hy,ly} and align y to x */
  if(ix >= -1022)
      hx = 0x00100000|(0x000fffff&hx);
  else {    /* subnormal x, shift x to normal */
      n = -1022-ix;
      if(n<=31) {
          hx = (hx<<n)|(lx>>(32-n));
          lx <<= n;
      } else {
    hx = lx<<(n-32);
    lx = 0;
      }
  }
  if(iy >= -1022)
      hy = 0x00100000|(0x000fffff&hy);
  else {    /* subnormal y, shift y to normal */
      n = -1022-iy;
      if(n<=31) {
          hy = (hy<<n)|(ly>>(32-n));
          ly <<= n;
      } else {
    hy = ly<<(n-32);
    ly = 0;
      }
  }

    /* fix point fmod */
  n = ix - iy;
  while(n--) {
      hz=hx-hy;lz=lx-ly; if(lx<ly) hz -= 1;
      if(hz<0){hx = hx+hx+(lx>>31); lx = lx+lx;}
      else {
        if((hz|lz)==0)    /* return sign(x)*0 */
        return Zero[(u_int32_t)sx>>31];
        hx = hz+hz+(lz>>31); lx = lz+lz;
      }
  }
  hz=hx-hy;lz=lx-ly; if(lx<ly) hz -= 1;
  if(hz>=0) {hx=hz;lx=lz;}

    /* convert back to floating value and restore the sign */
  if((hx|lx)==0)      /* return sign(x)*0 */
      return Zero[(u_int32_t)sx>>31];
  while(hx<0x00100000) {    /* normalize x */
      hx = hx+hx+(lx>>31); lx = lx+lx;
      iy -= 1;
  }
  if(iy>= -1022) {  /* normalize output */
      hx = ((hx-0x00100000)|((iy+1023)<<20));
      INSERT_WORDS(x,hx|sx,lx);
  } else {    /* subnormal output */
      n = -1022 - iy;
      if(n<=20) {
    lx = (lx>>n)|((u_int32_t)hx<<(32-n));
    hx >>= n;
      } else if (n<=31) {
    lx = (hx<<(32-n))|(lx>>n); hx = sx;
      } else {
    lx = hx>>(n-32); hx = sx;
      }
      INSERT_WORDS(x,hx|sx,lx);
      x *= one;   /* create necessary signal */
  }
  return x;   /* exact output */
}